1. Field of the Invention
This invention relates to ferrites and, more particularly, pertains to a new strontium ferrite borate.
2. Description of the Prior Art
As used herein, the term ferrite refers to compounds which can be described as oxides that contain iron (Fe) as a major constituent. Ferrites often have useful magnetic properties. For example, strontium hexaferrite, Sr0.6Fe.sub.2 O.sub.3 or SrFe.sub.12 O.sub.19, is an important material used in permanent magnets.
Closely related to strontium hexaferrite are barium hexaferrite and lead hexaferrite. As pointed out by Tokar, these three compounds form a continuous series of substitutional solid solutions. Thus, for example, lead (Pb) can replace strontium (Sr) in any proportion.
Besides permanent magnets, ferrites are used in such diverse applications as microwave and millimeter-wave devices, magneto-optical devices, and computer memories (core memories, magnetic tape, magnetic discs). Some ferrite applications require that the material be in single crystal form. Other applications can use, or may require, a polycrystalline or ceramic form.
Another kind of ferrite is iron borate, FeBO.sub.3. As pointed out by Andlauer et al, this material is one of only two known compounds which combine optical transparency in the visible spectrum with spontaneous magnetization at room temperature. Therefore, iron borate is of interest for magneto-optical devices.
Single crystals of ferrites have been prepared by a variety of techniques including growth from fluxes which contain lead oxide, PbO. Linares described the growth of single crystals of yttrium iron garnet and other ferrites from barium oxide-boron oxide fluxes and mentioned the use of lead oxide-boron oxide and strontium oxide-boron oxide fluxes. The methods he used involved slow cooling of the ferrite-flux solution. Linares teaches that the only phases which form from solutions comprising ferrites dissolved in strontium oxide-boron oxide fluxes are ferrites which contain no boron and strontium borates which contain no iron. There is no indication in Linares' work that a strontium ferrite borate phase can exist.